Making sense of the evidence for the “weekend effect”

In their analysis of 2013-14 English hospital administrative data, Freemantle and colleagues again find an increased risk of death in patients admitted at a weekend compared with weekdays.1 Their analysis combines both emergency and elective admissions and updates their earlier study.2 They confirm a persistent “weekend effect” in England, which they claim is “not otherwise ignorable,” and add to a substantial body of literature demonstrating this phenomenon both nationally3 4 5 and internationally.6 7 8

The findings of such studies and the resultant media coverage are being used by politicians to bring about changes in working practices,9 but against a strong background of criticism of these kinds of statistics.10 At first glance, there is conflicting evidence about whether the weekend effect exists at all.11 12 However, closer scrutiny shows that apparently “contradictory” studies tend to be smaller, carried out in single hospitals, and lack statistical power. Death after hospital admission, particularly for a planned surgical procedure, is relatively rare, and small studies simply don’t have the numbers to be able …